1) Field of the Invention
The present invention relates to a technique for controlling an unfolding operation of an air bag based on a distance between a person seated in a vehicle and a predetermined point.
2) Description of the Related Art
It is a common practice to detect a distance between an object and a predetermined point, and use the detected distance as a parameter to control something. For instance, it is known to control spreading out of an air bag in case of a car accident based on the distance between a passenger and a predetermined point.
In an air bag system, when a vehicle collision is detected, a balloon is blown by a constant explosive power. Japanese Patent Application Laid-open No. 2001-213268 discloses a technology to detect a distance between a predetermined position (a position of forward side of an occupant) and an occupant in a seat in a vehicle, and then control unfolding of an air bag based on the distance so as to protect the occupant from being injured by the air bag. For instance, if the distance is short, the air bag is made to unfold with weaker force for the safety of the occupant.
In Japanese Patent Application Laid-open No. 2001-213268, a spot beam light is irradiated to the occupant to acquire an image of the occupant. Based on the image, a distance between the occupant and the predetermined position is detected to judge the occupant position. Thus, it is possible to detect a distance between a part of the body of the occupant, which is irradiated by the spot beam light, and the predetermined position. However, although it is possible to detect a distance between a predetermined part of the body of the occupant and a predetermined position, it is impossible to detect a distance between the other parts of the body of the occupant and the predetermined position.
In other words, if the object can take various postures when seated on a vehicle, it may be possible to detect a distance between only a partial position of the occupant and the predetermined position; however, it is impossible to detect a distance between the other part of the object and the predetermined position. This may cause inappropriate control of the air bag system because of discordance between an actual position of the object and the detected distance.